Shared control channel structure

ABSTRACT

A shared control channel structure includes at least one control channel to be allocated at least to a user for at least one of uplink and downlink directions in a network, which the at least one control channel is arranged as at least a part of a modular structure comprising of modular code blocks on at least two different sizes. One of such modular structures may be represented as a tree structure in particular, where each of the modular code blocks define one node of the tree, respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.11/651,012, filed Jan. 9, 2007, which claims the benefit and priority ofU.S. Provisional Patent Application No. 60/878,079, filed Jan. 3, 2007.The disclosures of the prior applications are hereby incorporated byreference herein in their entirety.

FIELD OF THE INVENTION

The invention, according to various embodiments, relates to sharedcontrol channel structure including at least one control channel to beallocated at least to a user for at least one of uplink and downlinkdirections in a network, a method for creating at least one controlchannel, an apparatus comprising a transmitter for creating at least onecontrol channel, a receiver apparatus for receiving at least one controlchannel and a user equipment comprising a receiver for receiving atleast one control channel.

BACKGROUND OF THE INVENTION

In wireless communication systems, such as the long term evolution (LTE)of the Universal Mobile Telecommunications System (UMTS) TerrestrialAccess Network (UTRAN) in 3rd Generation Partnership Project (3GPP), newfunctionalities or features for data channels, such as fast linkadaptation, hybrid automatic repeat request, or fast scheduling in caseof high speed downlink packet access (HSDPA), rely on rapid adaptationto changing radio conditions. To implement these features, a controlchannel is used to carry control information relevant for those terminaldevices (or user equipments (UEs) in 3G terminology) for which data isavailable on the respective channel.

In particular, the LTE technology defines a packet radio system, whereall channel allocations are expected to happen in short periods ofsub-frames. This is motivated both by the packet radio technology butalso by the availability of wide transmission band and high symbol ratetransmission techniques, which enable high payloads even at short timeintervals. This is contrary to the prior art 3G systems, where dedicatedsignalling channels are necessary to be set up even for packet traffic.It is also different from the WLAN type of allocations, where each IPpacket transmission itself contains a transport header.

An adaptive coding concept may be applied to the control channel toexpand the dynamic range of the control channel. Adaptive modulation ofthe control channel may also be considered. Power control of the controlchannel is feasible, but only a constrained dynamic range can beexploited due to interference impacts and hardware limitations.

To support different data rates on the control channel a range ofchannel coding rates may be supported. Hence, at least two formats,e.g., of coding scheme may be supported for the control signaling viathe control channel. Adative modulation of the control channel is notnecessary, but is feasible to be included in addition to the adaptivecoding according to the invention, if necessary. The downlink (DL)control signaling may be located in the first n transmission symbols.Thus, data transmission in DL can at the earliest start at the sametransmission symbol as the control signaling ends.

FIG. 1 shows an example of a design of one “mother” control channel outof a plurality of control channels. This mother control channel can besplit into some “child” control channels by dividing the physicalresources using a variable coding scheme for allocations. In thisexample, the channel size of a “mother” control channel is 360 channelbits which may correspond to 180 QPSK (quadrature phase shift keying)symbols. However, it is noted that the number of channel bits is adesign parameter which may be used to adjust tradeoff between coverageand capacity. In FIG. 1, the upper part shows a case in which one useris allocated to the control channel, while the lower part shows a casein which two users are allocated within the same physical resources,each using a “child” control channel, corresponding to 180 channel bitsfollowing the abovementioned example. The control information conveyedvia the control channel may be divided into allocation information 42for the terminal device, a terminal identification 44 (e.g. userequipment identity (UEID), cell-specific radio network temporaryidentity (C-RNTI) etc.), and an error checking pattern 46 (e.g. cyclicredundancy check (CRC)). It is noted that the terminal identification 44and the error checking pattern 46 may be merged, such that a terminal oruser specific masking of at least a part of the error checking patterncan be achieved.

When decoding the control channel, the receiving end will have to knowthe size and/or length of the control symbol block (consisting ofcontrol information bits coded with the selected channel code rate)being decoded (in order to do channel decoding and error checks) priorto the actual interpretation of the information bits (i.e. contentdecoding). To illustrate, a situation is assumed where downlinkallocation uses 80 bits. In the upper case of a single user and achannel size of 360 channel bits, an effective code rate of about 0.2(i.e. 80/360=0.22), while in the lower case the effective code rate isincreased to about 0.4, by reducing the channel size to 180 bits andstill keeping the downlink allocation size to 80 bits. Now, if there aretwo formats available for the control signaling, the amount of users fordownlink using format #1 and format #2, respectively, must be determinedin order to know the size of each. The same applies to the allocationsfor the uplink direction. This information could be forwarded forexample as separate category 0 (Cat0) information (control informationfor the control channel).

In particular in the enhanced universal terrestrial radio access(E-UTRA) air interface and B3G technologies, all data carrying resourceallocations are signalled in downlink control channels, which arepresent in the first multi-carrier symbols of the sub-frame precedingthe multi-carrier symbols of the data channels (of downlink and ofuplink), wherein the control channels are separately coded.

In the prior art, the signalling channels may be received by followingknown channelization code sequences having a fixed spreading factor in adirect sequence spread spectrum system. These channelization coderesources form a channel, which is time multiplexed for different UEs.Each UE following the known channelization code sequence may filter, byits UE specific identifier, for a match to find its time multiplexedactivity periods.

Alternatively in the prior art, a control channel is provided, which isdivided to consist of common signalling entries of UE groups so that thephysical resource allocations are commonly announced for all these UEsand the UEs occupying each physical resource block (PRB) are indexed byshort identifiers among that group.

SUMMARY OF SOME EXEMPLARY EMBODIMENTS

There is a need to provide an improved control signalling scheme, inparticular by efficiently creating a control channel structure andsignalling entries for allocations, which are provided for shortsub-frame periods.

In accordance with a first aspect of the present invention, there isprovided a control channel structure including at least one controlchannel to be allocated at least to a user for at least one of uplinkand downlink directions in a network, which the at least one controlchannel is arranged as a modular structure comprising modular codeblocks of at least two different sizes.

Preferably, the modular structure forms a tree, where each of themodular code blocks defines one node of the tree, respectively.

In accordance with a second aspect of the present invention, there isprovided a method for creating at least one control channel to beallocated at least to a user for at least one of uplink and downlinkdirections in a network, wherein the at least one control channel isarranged as a modular structure comprising modular code blocks of atleast two different sizes.

In accordance with a third aspect of the present invention, there isprovided an apparatus comprising a transmitter for creating at least onecontrol channel to be allocated at least to a user for at least one ofuplink and downlink directions in a network, so that the at least onecontrol channel is arranged as a modular structure comprising modularcode blocks of at least two different sizes.

In accordance with a fourth aspect of the present invention, there isprovided a receiver apparatus for receiving at least one control channelallocated at least to a user for at least one of uplink and downlinkdirections in a network, which the at least one control channel isarranged as a modular structure comprising modular code blocks of atleast two different sizes, comprising a searcher for searching for anappropriate code block in the modular structure of at least one controlchannel.

In accordance with a fifth aspect of the present invention, there isprovided a user equipment comprising a receiver for receiving at leastone control channel allocated to the user equipment for at least one ofuplink and downlink directions, which the at least one control channelis arranged as a modular structure comprising modular code blocks of atleast two different sizes, and further comprising a searcher forsearching for a user equipment specific identifier in the modularstructure of the at least one control channel.

Further advantageous embodiments are defined in the dependent claims.

According to an embodiment of the present invention, there may beprovided an apparatus creating a signalling channel structure ofseparately coded blocks forming a modular structure, e.g. a coding tree,and a receiver apparatus to search for control channels in the mentionedmodular structure i.e. a tree by its receiver specific radio networkidentifier and search algorithms.

Further, there may be provided means (in the transmitter) to create and(in the receiver) to receive unified signalling entry formats forcorrect operation of transmission and reception.

According to another embodiment of the present invention, the controlchannel forms a modular structure e.g. a coding tree of variable channelcode rates. The nodes of the tree may consist of signalling entriescoded by a given code rate. The signalling entries (of information bits)may be of different types and may have different Information BlockLength (IBL). Each signalling entry type may follow a unified entryformat. Each Information Block of a signalling entry may be coded, ratematched and modulated exactly to the sub-carrier symbols forming a codednode of the tree.

The receiver may include means to search for a UE specific MAC ID in thenodes of the control channel, e.g. a tree. This allows UE specificseparate coded control channels with limited and optimized number ofsearches, due to the modular structure of the control channels.

The eNB (E-UTRAN Node B) may comprise means to allocate the sub-carrierresources of multi-carrier transmissions flexibly between the controlchannels in a modular structure.

In accordance with the present invention, the control channel isimplemented as a tree, where each node of the tree consists of exactlyknown sub-carrier resources, which may comprise of a modulated codeblock, wherein however the system bandwidth is essentially not changed.The tree structure allows efficient search of a matching controlchannel, since it has been found that a search result at a given node ofthe tree allows deduction of candidate searches in the next higher levelof the tree. This is not feasible with other arbitrary but systematicmapping schemes. Without the modular structure e.g. a tree i.e. havingan arbitrary and systematic mapping of control channels to thesub-carrier resources, the number of required searches becomes large,which is not the case with the present invention.

The modular structure of the control channel(s) according to the presentinvention is advantageous in enabling searching and decoding processesby the user. In particular, the modular structure according to thepresent invention allows for a parallelization of the searching anddecoding processes (i.e. decoding simultaneously from multiple candidateplaces of channels, in particular physical downlink control channels,before knowing the results of decoding tests on other candidatechannels. Moreover, the modular structure according to the presentinvention renders it possible to search and decode in the controlchannels in any favoured order, in particular from the largest controlchannel to the smallest control channel, from the smallest controlchannel to the largest control channel, and from the control channel,whose SINR (signal-to-noise ratio with the noise including both formalnoise and interference) is closest to the expected SINR value at thereceiver (as the transmitter is expected to power control respectively),to the SINR deviating more from the expected SINR. Further, the presentinvention renders it possible to limit per each user the number of thesearching and decoding processes. The modular structure further allowsfor efficient usage of all sub-carrier resources available in thedownlink control signalling part of a sub-frame. A maximum number ofusers allocated per sub-frame may be provided depending on thetransmission resources required by their signalling. Moreover, adiscrete structure of control channels is created, despite of theirvariable information block length and (IBL) and effective code rate(ECR). Moreover, the modular structure according to the presentinvention allows for a transport of each control channel, in particularphysical downlink control channel, by a defined modulation, by aneffective code rate selected from a defined effective code rate set, bypower balancing of sub-carriers between the other control channels, bypower addition of the control channel from un-used sub-carriers, and/orby a large amount of frequency diversity. Finally, the present inventionmay result in reasonable limitation per user to the configurability ofthe control channels which each user is mandated to code.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described based on embodiments withreference to the accompanying drawings in which:

FIG. 1 schematically shows a principle example of a control channeldesign using variable coding schemes;

FIG. 2 shows a schematic diagram indicating channels used forcommunication in an enhanced wireless network;

FIG. 3 is a schematic diagram showing the time multiplexing of downlinkcontrol signalling and shared data transmission resources of onesub-frame according to an embodiment;

FIG. 4 shows a schematic diagram of an arrangement of a plurality ofphysical downlink control channels in a modular structure according toan embodiment;

FIG. 5 shows a schematic diagram of a physical downlink control channelin a tree of code blocks arrangement according to an embodiment;

FIG. 6 shows a schematic diagram of a physical downlink control channelin a tree of code blocks arrangement with three allocated nodes indifferent levels of the tree according to an embodiment;

FIG. 7 shows an example of a tree with three allocated nodes mapped tosub-carrier resources in a distributed manner according to anembodiment;

FIG. 8 shows a schematic diagram of the distribution of control channelsover the system bandwidth to one, two or more OFDM (orthogonal frequencydivision multiplexing) symbols in a sub-frame according to anembodiment;

FIG. 9 shows a schematic diagram of the distribution of control channelsover the system bandwidth to three OFDM symbols in a sub-frame accordingto another embodiment;

FIG. 10 is a schematic diagram showing that the system bandwidth isdivided to an integer number of modular PDCCHs according to anembodiment;

FIG. 11 schematically shows an example of the modular structure ofPDCCHs of FIG. 10;

FIG. 12 schematically shows a more general example of the modularstructure of PDCCHs represented as a tree according to anotherembodiment;

FIG. 13 shows a schematic diagram of a physical downlink control channelin a tree of code blocks arrangement in case of a wide system bandwidthwherein the allocated three levels of the tree are higher in the tree(from the root of the tree) compared to a tree on a narrow systembandwidth according another embodiment;

FIG. 14 shows a schematic diagram of rate matching of signalling entriesto a modular structure of PDCCHs according to an embodiment; and

FIG. 15 shows a schematic block diagram of a computer-basedimplementation according to an embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, various embodiments of the invention will be describedbased on a wireless transmission system, such as evolved UTRA (E-UTRA).The embodiments of this invention are not limited for use with only thisone particular type of wireless communication system, and that they maybe used to advantage in other wireless communication systems such aswireless ad hoc networks, cognitive radios, beyond third generation(B3G) systems and fourth generation (4G) systems, as non-limitingexamples.

As a non-limiting example, mathematical transforms may be used to createmulti-carrier symbols. As non-limiting examples of such mathematicaltransforms, an OFDM multicarrier signal may be generated by discreteFourier transforms or by fast Fourier transforms. Other non-limiting,exemplary transforms that may be used to generate multicarrier signalsinclude cosine transforms, sine transforms, filterbank transforms andbi-orthogonal transforms. The properties of these transforms differ fromthe properties of OFDM, but they may be applied similarly to create amulticarrier transmission. Even blocked transforms or interleavedtransforms (IFDMA) may be used to create similar transmission schemes,where a block of symbols is available on a number of frequency bins at atime. In reference to E-UTRA technology, the terms “multicarrier symbol”and “OFDM symbol” are used interchangeably. For other B3G technologies,the term “multicarrier symbol” may be considered more generic.

FIG. 2 shows a schematic diagram of a general network and channelarchitecture in which the invention, in an exemplary embodiment, can beimplemented. A radio access network provides access to a UE 10 via anaccess device 20, e.g., a base station device, a node B, or an accesspoint, having a scheduler functionality for scheduling resources byallocating physical resource blocks to users which have connectivity tothe access network. Data and control signalling is performed usingspecific channels indicated in FIG. 2.

A DL shared channel (DSCH) 100 is provided as a shared transportchannel, which means that the available bandwidth is flexibly anddynamically shared among the served active users. Fast scheduling infrequency shares the DSCH 100 for a period of a sub-frame among theusers, scheduled in time, from the set of all served users. Thisexploits multi-user diversity and allocates more bandwidth to users withmore demand and allocates more bandwidth with more favourable radioconditions to each user. A scheduler can base its decisions for exampleon predicted channel quality (in time and in frequency), the currentload of the cell and the traffic priority class (real-time ornon-real-time services). Additionally, a physical downlink sharedchannel (PDSCH) 120 is provided as a physical channel for carryinghigh-speed bursty data to users. Similarly, a uplink shared channel(USCH) 200 is provided as a shared transport channel, and a physicaluplink shared channel (PUSCH) 220 is provided as a physical channel forcarrying high-speed bursty data from users. Feedback information (e.g.acknowledgements, channel information etc.) in the uplink (UL) directionfrom the UE 10 to the access device 20 is signalled via a physicaluplink control channel (PUCCH) 300.

Additionally, a physical downlink control channel (PDCCH) 400 isprovided as a physical signalling channel to convey control informationrelated to at least one of the PDSCHs 120 in downlink and PUSCH inuplink directions or to perform hybrid automatic repeat request (HARQ)signalling.

The transmissions on downlink and uplink may apply a frequency divisionduplex or time division duplex arrangement.

Fast link adaptation enables the use of more spectrally efficientmodulation when channel conditions permit. With favourable channelconditions 16 quadrature amplitude modulation (QAM) or even 64 QAM maybe used for example, while QPSK may be used when unfavourable or lessfavourable channel conditions or large penetration loss are faced, orwhen a wide area coverage is expected.

Additionally, the coding rate may be adapted, wherein a coding rate of ¼means that error correction and detection takes 75 percent of thebandwidth and the user data rate is only 25 percent of the coded symbolrate. Likewise, a coding rate of 4/4 means that the user achieves themaximum data rate, but there is no error correction, and therefore manyerrors are expected in the received data, which decreases the throughputdue to error recovery retransmissions.

As an additional measure, adaptive modulation and coding (AMC) schemesmay be used for link adaptation. These schemes enable the system tochange the coding and modulation schemes. The channel condition has tobe measured or estimated based on the feedback of the receiving end.Links with better transmission conditions can be assigned a higher ordermodulation scheme and higher coding rates. The benefits of AMC includeavailability of instantaneously high data throughput and high efficiencywith low interference variation because it is based on modulation andcoding adaptation instead of e.g. variations in transmit power.

Link adaptation is the process of modifying transmission parameters toadapt to the experienced channel parameters. Higher order modulation, inconjunction with channel coding, optimizes the use of a fading radiochannel. By transmitting at constant power, the modulation and codingschemes (MCS) can be selected to maximize throughput. A media accesscontrol (MAC) layer functionality at the access device selects the MCSthat matches the instantaneous radio conditions depending on a shorttransmission time interval (TTI) and depending on the selected frequencyresources selected for the payload. This applies similarly for downlinkand uplink transmissions, even in case their MCS choices areindependent. The MCS selection may depend on for example channel qualityindication, instantaneous power of the physical channel, quality ofservice (QoS) demands of the requested service, or experienced bufferingqueue sizes.

In an embodiment, a limit is put on the MCS format settings for thephysical downlink control channel PDCCH 300 such that it is onlypossible to fit an integer number of allocations within a fixed numberof sub-carriers (in the system bandwidth) on a given number ofmulticarrier symbols (in time dimension). That is, basically, a knownset of sub-carriers are reserved for each allocation for a downlinksignalling, for an uplink signalling or for signalling both of them inthe same PDCCH. Then, if a user being allocated is in a poor channelcondition, the MCS will be set such that all sub-carriers will be usedfor this user. That is, the mother control channel is fully allocated tothis user. If e.g. the channel conditions for other users are such thattwo or more users will fit within the mother control channel (i.e. setof sub-carriers), it will be split into a multiple of child controlchannels, so that these users will share the allocation set ofsub-carriers of the mother control channel, while separate coding maystill be used for each user so that they use a less robust MCS for theirresource allocation information present in one of the child controlchannels.

Hence, a full downlink signalling resource available as a number ofsub-carrier symbols (up to all sub-carrier symbols available in thesystem bandwidth) on a defined multicarrier symbols of the sub-frame (upto all multicarrier symbols of the sub-frame) can be split into aplurality of control channels. These downlink signalling resources willconsist an integer number of mother control channels and a respectivelarger integer number of child control channels.

These structures will allow several possible alternatives ofallocations. E.g., in the sub-carrier resources where a mother controlchannel is allocated, there are no feasible allocations on the childcontrol channels. Similarly, in the sub-carrier resources where mothercontrol channels are not allocated, it is possible to have a largernumber of allocations on the respective child control channels. A singlemother control channel can then individually be split into child controlchannels. Thus, any mixture of allocations consisting of a number ofmother control channels and a number of child control channels may befeasible as long as each of the sub-carrier symbols are modulated by aunique symbol content. There exists a versatile number of allocationspossible in the modular control channel structure consisting of largenumber of sub-carrier resources. Even for a smaller number ofsub-carrier resources available (e.g. due to limited system bandwidth),a more limited number of allocations will be possible, but still theirversatile arrangement is feasible according to the modular controlchannel structure.

Every downlink sub-frame is time multiplexed to consist of downlinkcontrol signalling resources and the physical downlink shared channel(PDSCH). The downlink control signalling precedes the shared datatransmission resources of the downlink and the uplink, as shown in FIG.3. These downlink control signalling resources actually may carrymultiple Physical Downlink Control Channels (PDCCH), each of whichcarries information for one MAC ID. This means that for each UE thesignalling blocks are separately coded.

The multiple control channels are proposed to be arranged as a modularstructure of code blocks of different sizes in terms of used physicalchannel bits, as shown in FIG. 4, such that a control channel of thelargest code block may be replaced by up to two control channels of halfthe size. Further, one control channel of half the size may be replacedby up to two control channels of quarter the size of the largest codeblock. Due to the arrangement as a modular structure, the UE is able tofind the candidate PDCCHs efficiently from a possible set ofalternatives. As different signalling entry types (e.g. a downlinkallocation, an uplink allocation, etc.) are of different informationblock length (IBL) and they are possibly encoded with a differentchannel code rate for different UEs, their usage of sub-carrier symbolresources varies a lot.

The structure is alternatively presented as a tree as shown in FIG. 5wherein the largest code block is named “CB1”, the control block of halfthe size of CB1 is named “CB2”, and the code block of quarter the sizeof CB1 is named “CB3”. Each code block is called a control channel as itcarries information for one MAC ID. The MAC ID is used by a UE or by agroup of UEs to detect the channel. At each level of the tree, each noderepresents a single control channel of a code block, which may consistof an information block of given length (information block length IBL)coded with an effective code rate (ECR). The number of the controlchannels at the lowest level of the tree is determined by the systembandwidth and number of OFDM symbols (n) available for the largest codeblocks. Any node of the tree, which is not occupied by a control channelin this level, is available for the next level of the tree as twocontrol channels, each of which are half of the size of the controlchannel at the parent node.

The system bandwidth consisting of a given number of sub-carrierresources may be divided into an integer multiple of control channels.In the embodiment of FIG. 5, a given node of the tree, i.e. a set ofsub-carriers, can consist of one control channel of the largest codeblock, of up to two control channels of the second largest code blocksor up to four control channels of the smallest code blocks. Here, it isassumed that each code block of the lower level in the tree is doublethe size of the code block in the previous higher level in the tree.Rate matching is used to adjust the IBL with the selected code rateexactly to the sub-carrier resources forming a node of the tree. In casesome nodes do not contain any control channel, the sub-carriers are thusnot modulated with data and do not consume transmission power.

FIG. 6 schematically shows an example of a tree with three allocatednodes (one defined by CB1, another one defined by CB2, and yet anotherone defined by CB3) in different levels of the tree.

FIG. 7 schematically shows an example of a tree with three allocatednodes (one defined by CB1, another one defined by CB2, and yet anotherone defined by CB3) mapped to the sub-carrier resources in a distributedmanner. The PDCCH is distributed over the system bandwidth. Each codeblock on the PDCCH is distributed to a set of sub-carriers. E.g. CB1consist of CB11, CB12, CB13, CB14; CB2 consists of CB21, CB22, CB23,CB24; and CB3 consists of CB31, CB32, CB33, CB34. In FIG. 7, “RS (A1)”and “RS (A2)” show the presence of reference symbols for two antennas inthe first OFDM symbol of the sub-frame.

Each control channel extends entirely over the first n OFDM symbols,which are available for the control channels, as shown in FIG. 8. ThePDCCHs are entirely frequency multiplexed to the sub-carriers on all ofthe OFDM symbol resources available for control signalling, as alsoshown in FIG. 8. This enables efficient power balancing between thePDCCHs so that each of them meets the expected SINR at the intended UEreceiver.

As frequency diversity is known to provide gains, every PDCCH mayactually be proposed to be modulated to a distributed set ofsub-carriers as shown in FIG. 7, instead of constitutive ones as shownin FIG. 8.

Actually the control channels are distributed over the system bandwidthto the sub-carriers on one, two or three OFDM symbols in that sub-frame,to maximize the frequency diversity so that there are e.g. fourdistributed sets of sub-carrier re-sources allocated per eachcode-block. This is illustrated in FIG. 9.

FIG. 10 is a schematic diagram showing an embodiment wherein the systembandwidth is divided to an integer number of modular PDCCHs. FIG. 11gives an example of a tree representation of the structure shown in FIG.10, wherein each node of the tree corresponds to a defined set ofsub-carriers. A more generic representation of a tree structure, whichis compatible to that of FIG. 4 (with n1=3), is given in FIG. 12,wherein again each node of the tree consists of an exactly defined setof sub-carriers.

FIG. 13 schematically shows a further example of a tree on a wide systembandwidth wherein the allocated three levels of the tree are much higherin the tree compared to a tree of a narrow system bandwidth as e.g.shown in FIGS. 5 to 8 and 10 to 12.

As each control channel has to be uniquely identified by a MAC ID, itcan be combined to the CRC by partly masking the CRC bits with theMAC-ID. As the MAC ID is used for addressing both UE specific controlchannels and common control channels, it is reasonable to define the MACID in a compatible way. MAC IDs are reserved from the C-RNTI addressspace. Thus, reception of any control channel is possible by filteringcontrol channels with the respective MAC ID. An error detection isavailable from the MAC ID masked CRC. The length of the MAC ID ismatched to the C-RNTI length of 16 bits, but the CRC may be selected tobe 16 or 24 bits.

The identification of an individual UE in a cell is based on the C-RNTI,which is signalled to the UE when changing from a LTE idle state to aLTE active state or when making a handover to a new cell. Thus, theC-RNTI can be directly used as the MAC ID of a control channel for anindividual UE.

For paging signalling, a commonly available MAC ID is assigned (calledPG-RNTI). This may be informed in the system information. Thus, any UEmay filter possible paging allocations in sub-frames belonging to itsDRX (discontinuous reception) active cycle by the commonly known MAC IDavailable for the PCH (paging control channel). The PCH itself ismodulated to the data part of the sub-frame.

The identification of a control channel for a RACH (random accesschannel) response is derived from the resources used for the RACH burstcreation by the UE. Thus, the RACH sub-frame, the RACH frequencyresource and the RACH preamble index can together be applied todetermine the MAC-ID (called RA-ID for the case of RACH response) to letthe UE receive the RACH response in any one of the downlink sub-framesfollowing that RACH transmission.

The identification of a group of UEs in a cell is based on assigninggroup IDs from the C-RNTI address space. Thus, a UE may have both itsindividual C-RNTI and a group ID valid simultaneously and may filter theMAC ID for the reception of a control channel with either the C-RNTI,with the group ID or with both of them.

There exist different types of signalling entries on the controlchannels. Each entry type follows a given bit exact format and has adefined relation to the other formats. It will be possible to providefuture signalling entries or modify the existing ones. This may requirechanges to the known rate matching factors to fit them to the modularcontrol channel structure e.g. to the nodes of the tree.

So, as different signalling entry types need to be defined (e.g. for adownlink allocation, an uplink allocation etc.), their IBL may not beequal since each of them is minimized in bits as much as feasible. Inorder to keep the coded PDCCH structure modular, any given signallingentry has to be rate matched to the exact set of sub-carrier resourcesselected for that PDCCH. Rate matching guarantees that the symbolresources of the PDCCH are exact and modular as shown in FIG. 14,wherein the largest signalling entries for the lowest ECR are met to thelargest PDCCH (PDCCH#k). Those coded ones with a higher ECR are mappedto the PDCCHs of half the size of the largest PDCCH (as PDCCH#k1). Thesmallest signalling entries with the highest code rate are mapped to thesmallest PDCCHs (as PDCCH#k11). If they apply to a lower code rate, theyare mapped to the double size PDCCH (as PDCCH#k2).

The flexibility of rate matching is a large benefit, because thesignalling entry types anyway need to be standardized exactly. Now, anyfuture update to the signalling fields would cause problems in thelegacy decoders searching for PDCCHs of presumed size. However, due tothe modular structure, the code block sizes are kept constant even withthe future updates and just new rate matching factors have to bestandardized respectively. Thus, the modular structure is possible to besearched through consistently both by the previously defined ratematching factors and newly defined rate matching factors. All the codeblocks realizing the previously defined (legacy) rate matching factorscan be found normally despite of possible presence of entries with thenew rate matching definitions. Vice versa, the code blocks realizing newrate matching factors can be found normally despite of possible presenceof entries with the old rate matching definitions.

Types of signalling entries may at least be

-   -   downlink signalling entry,    -   uplink signalling entry,    -   paging signalling entry,    -   RACH response signalling entry,    -   uplink acknowledgement signalling entry, and/or    -   Cat0 signalling entry.

Further types of signalling entries may at least be

-   -   downlink group signalling entry wherein VoIP (voice over IP        (internet protocol)) is the main driver,    -   uplink group signalling entry wherein VoIP is the main driver,        and/or    -   downlink signalling entry for two code word MIMO (multiple input        multiple output).

The proposed bit-fields for downlink signalling entry may include

-   -   UE dedicated MAC ID (identification by the C-RNTI [16 bit]),    -   CRC [8 bit] (in addition to UE ID masked CRC of 16 bits) wherein        for narrowband CRC [0 bit] is sufficient,    -   indicator of the allocated physical resource [DLAbw bit]        depending on the bandwidth wherein any PRBs can be flexibly        allocated and F-FDM-various optimization schemes are proposed,    -   transport format of the allocation [5 bit],    -   HARQ control information [5 bit] wherein the asynchronous HARQ        may comprise a 3-bit HARQ process number and/or 2-bit redundancy        version (a bit combination acts as a new data indicator), and/or    -   other information, MIMO etc.

The proposed bit-fields for uplink signalling entry may include

-   -   UE dedicated MAC ID (identification by the C-RNTI [16 bit]),    -   CRC [8 bit] (in addition to UE ID masked CRC of 16 bits) wherein        for narrowband CRC [0 bit] is sufficient,    -   indicator of the allocated physical resource [ULAbw bit]        depending on the bandwidth wherein only adjacent resource units        can be allocated to one UE, wherein indexes of the first and the        last resource units are signalled and/or an actually index of        the first RU and the number of allocated RUs would be shorter or        equally short than the above, but result in variable fields,    -   duration of allocation [2 bit] which can be embedded to the        other bit fields, e.g. TFI in this case, and may be needed        specially for the RRC_Connection_Request message in coverage        critical situations (as segmentation is not allowed),    -   transport format of the allocation [5 bit],    -   HARQ control information [2 bit] wherein the synchronous HARQ        may comprise a 2-bit redundancy version (a bit combination acts        as a new data indicator),    -   power control [5 bit] every kPC sub-frames,    -   timing advance [4 bit]—every kTA sub-frames, and/or    -   other information, MIMO etc.

The proposed bit-fields for paging signalling entry may include

-   -   paging dedicated MAC ID, PG-RNTI [16 bit]    -   CRC [0 bit] (UE ID masked CRC of 16 bits)    -   indicator of the allocated physical resource [PGAbw bit]        depending on the bandwidth with a diversity transmission of PRBs        over the system bandwidth up to 600 sub-carriers, and/or    -   transport format of the allocation [5 bit].

The proposed bit-fields for RACH response signalling entry may include

-   -   RACH response specific MAC ID, RA-ID [16 bit] wherein the RA-ID        in-dude a preamble index part for the time, frequency and        sequence index of the RACH burst    -   CRC [0 bit] (RA-ID masked CRC of 16 bits)    -   timing Advance Long [10 bit], and/or    -   power setting [5 bit].

The proposed bit-fields for uplink acknowledgement (ACK) signallingentry may include

-   -   a HARQ ACK/NAK (negative acknowledge character) list in the        order of the previous uplink allocations [max number of        ACK/NAKs] with 1 bit per previous allocation.

The previous uplink allocations of a sub-frame (k−Δk) are acknowledgedin a given downlink sub-frame (k) after a fixed delay (˜1.5 or 2.5 ms tobe defined) in a list format. For decoding an AN (ACK/NAK) bit in thesub-frame (k), it is sufficient for a UE to know in which node theallocation was given (in sub-frame k−Δk).

It is to be noted that many of the bit-fields are bandwidth dependent,e.g. the UE-identification and CRC in total may consist of 16 bits fornarrowband and up to 24 bits for wideband. Also allocation indicationdepends largely on the bandwidth, as maximum of 6 bits are sufficientfor 1.25 MHz bandwidth, but 100 bits were needed in maximum for 20 MHz.This is why the number of bits required to signal the allocation in abandwidth dependent way is noted here as DLAbw of downlink allocation asa function of the system bandwidth, ULAbw of uplink allocation as afunction of the bandwidth and PGAbw of paging allocation as a functionof the system bandwidth.

An entry ID may be necessary, unless the entry type can uniquely berecognised from its IBL and/or type of the MAC ID. Paging entry may beuniquely recognized from its MAC ID wherein PG-RNTI does not match withany UE specific C-RNTI. The RACH response entry may be uniquelyrecognised from its MAC ID wherein RA-ID does not match with any UEspecific C-RNTI. Thus, the downlink signalling entry, the uplinksignalling entry, the downlink group signalling entry, the uplink groupsignalling entry may require an entry ID.

The tree is dimensioned so that the lowest level of the tree containsenough nodes to support the required maximum number of most robust codeblocks on the deployed system bandwidth. These code blocks determine themaximum number of ‘cell edge’ users per sub-frame. On the other hand,the tree must contain enough nodes to enable allocations up to themaximum number of users per sub-frame. The depth of the tree isdetermined by the product of the number of IBLs and number of code ratesavailable.

In a preferred embodiment there are at least two clearly different IBLsand at least two different code rates so that the depth of the tree isat least 3. All the other IBL tunings can be satisfied by rate matchingas explained below.

Once the maximum size of the tree is known, it is calculated to how manyOFDM symbols (in maximum) it is mapped onto. This depends on the systembandwidth, as the sub-carrier resources are largely different fordifferent bandwidths.

The tree may be pruned so that all the nodes are not possible to beallocated in all the levels of the tree. Still, all the sub-carriersavailable are possible to be allocated. The pruned tree can be signalledeasily by indicating, which nodes at which level of the tree areactually available for allocations. (this is a common information forthe transmission and may be statically signalled e.g. in the systeminformation messages.) Pruning will just reduce the number of possibleallocation combinations so that the search complexity for the UEs isreduced. Despite of the pruning, there will remain a sufficient and evenoverwhelming number of PDCCH combinations available. The opportunitiesand also the needs of pruning appear more for a wideband system than fora narrower bandwidth.

As searching in the tree, even the pruned one, takes UE processing time,it may be feasible to decide a sub-set of nodes, which each UE isexpected to decode for detecting any of its allocation. This UE specificset of nodes of the tree may be signalled to the UE in advance by theradio resource control (RRC) signalling e.g. during the initial access.The number of nodes (control channels) to decode may partly depend onthe UE capability. Any UE however has to be able to decode the possiblecode blocks of the paging entry, the AN entry and a given number ofalternative nodes for downlink and uplink signalling entries. The numberof control channel positions for downlink and uplink signalling entrieshave still to include several alternatives at different levels of thetree (effective code rates), so that the flexibility of the signallingchannels does not bind the signalling choices for the decisions made bythe PDSCH scheduler. It is proposed that at least four code blockpositions will be searched by all the UEs.

As described above with reference to the FIGS. 3 to 13, the controlchannels are dimensioned so that they form a binary tree i.e. the mostrobust channel coding format for the longest information block length(IBL) is divisible to 2× multiple code blocks depending on the depth ofthe tree.

The longest IBL is the downlink signalling entry, because it needs toallow flexible frequency multiplexing (F-FDM) scheme and asynchronousHARQ processing, which consume more bits than signalling for any othertype of allocation. Thus, the downlink signalling entry coded with thelowest ECR will be designed to occupy one mother PDCCH. If the IBL ofthe uplink entry is close to the downlink entry, it will also occupy amother PDCCH. If uplink entry is significantly smaller, e.g. close to0.5*IBLDL, the uplink entry will be rate matched to one of the childPDCCHs. If downlink and uplink allocations, however, are designed to bepossible to be placed to the same PDCCH, those will occupy a motherPDCCH instead. In this case, independent downlink signalling entries anduplink signalling entries will occupy one of the child PDCCHs each.

The most robust coding is selected from a set of 2× code block sizes{ECR0, ECR1}, e.g. of order {⅙, ⅓} or {⅛, ¼} or {⅛, ½}. By increasingthe depth of the tree, also more code rate options are available, butthis significantly increases the expected search process in the tree.Some choices may favour even more code rates as {⅙, ⅓, ⅔} or {⅛, ¼, ½}.

The uplink signalling entry contains an IBL being about half of the sizeof the downlink signalling entry This is because in uplink only adjacentfrequency multiplexing (A-FDM) allocation scheme is allowed. Further,the synchronous HARQ processes of uplink require less signalling. On theother hand, power control and timing advance may change the IBL to beclose to equal to the downlink entry. An uplink entry may use ECR0 orECR1 per UE.

The paging code block always requires a distributed transmission formatto maximize its frequency diversity. Further, it does not include HARQprocesses so that its signalling entry IBL is shorter than that of adownlink entry. The paging code block may be rate matched to the size ofthe most robust downlink code block, so that ECR0 is selected, but dueto rate matching a slightly lower code rate will result. Alternatively,the paging code block may be rate matched to the size of the less robustdownlink code block, so that ECR1 is selected, but due to rate matchinga slightly higher code rate than ECR0 but a lower code rate than ECR1will result. There is at maximum one paging signalling entry needed persub-frame, because there is at maximum one PCH (paging channel)transport channel per sub-frame, which carries the paging messages ofall the paged UEs.

The IBL of the RACH response signalling entry is close to equal size ofthe IBL of the other smallest entries. The RACH response may apply ECR0or ECR1 respectively, because the RACH preamble is expected to indicatethe rough CQI (channel quality indicator) level for the downlinktransmission. There may be more than one RACH response signallingentries per sub-frame.

The downlink signalling entry of the uplink acknowledgements (AN codeblock) is a list format of positive or negative acknowledgements per UEallocation in the uplink sub-frame in a past sub-frame (k−Δk) precedingthe current sub-frame (k). Each UE that had an allocation in sub-frame(k−Δk) will need to decode the common AN code block in sub-frame k. Theposition of the acknowledgement bit of each UE in the AN list field isdetermined by the position of that signalling entry in the tree, whichhas signalled the uplink allocation for the UE in sub-frame (k−Δk). Asthe tree is common, each UE will uniquely know the position of itsallocation in the tree.

If the IBL sizes of the downlink and uplink allocations do notefficiently fit to the same binary tree, i.e. the IBLDL˜2*IBLUL orIBLDL˜IBLUL does not hold, it may become reasonable to constructseparate trees for the downlink and uplink allocations, respectively.

It is proposed here that even if the IBL of different signalling entriesdoes not exactly match to the 2× structure of the tree, the tree isconstructed by rate matching. Thus, every signalling entry coded withECR0 or ECR1 will be rate matched to force an exact fit to a controlchannel in the node of the tree. Regarding the rate matching, the sameholds for other possible modular choices of a control channel structurethan a tree.

As the tree structure requires the control channels to be 2× structured,there are preferably three ways of achieving this:

-   -   The bit-field design of the signalling entries is such that the        IBL of each entry is dimensioned properly to follow the 2×        structure.    -   Some extra RFU (reserved for future use) bits are added to the        signalling entries to properly fulfil the 2× structure.    -   The IBLs are of arbitrary but known length and do not follow the        2× structure directly, but still the code blocks do. This is        achievable by rate matching the IBL with a given code rate to        the 2× structure. The penalty of this is that the rate matching        factor also has to be blindly detected by the receiver. However,        as the signalling entries and their IBL are known, there is also        a known limited set of rate matching factors to search for.        Another advantage is that the rate matching has to be done at        limited nodes of the tree only.

It is possible to provide future signalling entries or modify theexisting ones due to the modular structure of the PDCCHs. The possiblechanges to the signalling entries may require introduction of new ratematching factors, but that is considered a small effort. Compatibilityto the earlier implementations is well preserved, as the modular controlchannel structure is possible to be searched through—both by thepreviously defined rate matching factors and by the newly added ratematching factors. All the code blocks realizing the previously definedrate matching factors can be found normally despite of the presence ofentries with new rate matching definitions. Vice versa, the code blocksrealizing new rate matching factors can be found normally despite of thepresence of entries with old rate matching definitions.

Any code block may have any required power boosting, if the meantransmission power per OFDM symbol is kept constant. Power boosting mayhappen by exploiting the power available from the non-used symbolresources or between different code blocks of control channels assignedto different UEs. Demodulation of the control channel by QPSK anddecoding of the control channel by a convolutional code are feasibleoperations without knowing the signal amplitude relative to the pilotsymbols. Thus, power boosting is a practical solution, which does notrequire any specific signalling in this case. Any unused sub-carriersymbol resources do not create any inter-cell interference to theirco-channel symbols in the neighbouring cells.

The UE receiver is configured to search for allocation information fromthe PDCCHs mandated for it. However, there are many dependencies that donot require the UE search for all the signalling entries all the time.Such dependencies may include the UE state, the UE capability orknowledge of UE's active traffic flows.

In the LTE idle state, the UE only searches for paging signallingentries and does not need to apply other rate matching factors in itssearch.

If the UE created a RACH burst, it will search for RACH response andneed not apply other rate matching factors in its search.

In a typical LTE active state operation, the UE does not need to searchfor rate matching factors of the paging entry nor the rate matchingfactors of the RACH response entry. The UE just needs to search for ratematching factors of the downlink entry and uplink entry.

It may be feasible that also downlink group entry and uplink group entryare defined for VoIP usage. Thus, if the UE has a VoIP session active,it will have to search rate matching factors both for downlink anddownlink group entries and rate matching factors for uplink and uplinkgroup entries.

Further, if the UE is dual codeword MIMO capable, it needs to searchrate matching factors for the downlink MIMO signalling entry, if this isseparately defined. However, in this case it is proposed that allsignalling for this UE follows the MIMO entry format, and thus it wouldnot need to search for regular downlink signalling entries at all.

Despite there are many different rate matching factors feasible in thenodes of the tree, the tree will be so defined that each UE will onlyneed to search for those rate matching factors relevant for its expectedsignalling entry formats.

FIG. 15 shows a schematic block diagram of a software-basedimplementation of the proposed advanced decoding procedure. Here, the UE10 of FIG. 2 comprises a processing unit 210, which may be any processoror computer device with a control unit which performs control based onsoftware routines of a control program stored in a memory 212. Programcode instructions are fetched from the memory 212 and are loaded to thecontrol unit of the processing unit 210 in order to perform theprocessing steps of the functionalities as described above. Theseprocessing steps may be performed on the basis of input data DI and maygenerate output data DO, wherein the input data DI may correspond to thereceived control information of the PDCCH 300 and the output data DO maycorrespond to the decoded allocation information. Consequently, theinvention may be implemented as a computer program product comprisingcode means for generating each individual step of the decoding procedureaccording to the embodiment when run on a computer device or dataprocessor.

In summary, a control channel structure includes at least one controlchannel to be allocated to a user for at least one of uplink anddownlink directions in a network, which the at least one control channelis arranged as a modular structure comprising of modular code blocks onat least two different sizes. One of such modular structures may berepresented as a tree structure in particular, where each of the modularcode blocks define one node of the tree, respectively.

It is apparent that the invention can easily be extended to any kind ofcontrol channel where adaptive coding or modulation or other types offormats are used. Any pattern or sequence may be used for selecting andtesting available types of formats. The described embodiments arerelated to control signaling via wireless channels. However, theinvention, according to various embodiments, can be applied to controlsignaling via wired channels as well. Additionally, the invention can beapplied to any device, apparatus, module or integrated chip where acontrol information is to be decoded. Exemplary embodiments may thusvary within the scope of the attached claims.

We claim:
 1. A receiver apparatus for receiving at least one controlchannel allocated at least to a user for at least one of uplink anddownlink directions in a network, which the at least one control channelis arranged as at least a part of a modular structure comprising modularcode blocks of at least two different sizes, said receiver apparatuscomprising a searcher for searching for an appropriate code block in themodular structure of the at least one control channel, wherein themodular structure forms a tree where each of the modular code blocksdefines one node of the tree, respectively, wherein each of the nodescomprises signalling entries coded by a given code rate, wherein themodular structure of the at least one control channel allows userequipment specific separate coded control channels with limited andoptimized number of searches, and wherein the signalling entries includeinformation blocks, and each information block of a signalling entry israte matched to a node of the tree.
 2. The receiver apparatus accordingto claim 1, wherein the searcher is configured to search for anappropriate code block by using an identifier specific to the receiverapparatus.
 3. The receiver apparatus according to claim 1, for receivingthe at least one control channel whose modular structure forms a treewhere each of the modular code blocks defines one node of the tree,respectively, wherein the searcher is configured to search in the nodesof the tree for a specific identifier to be associated to the receiverapparatus.
 4. A user equipment comprising a receiver for receiving atleast one control channel to be allocated to user equipments for atleast one of uplink and downlink directions, which the at least onecontrol channel is arranged as at least a part of a modular structurecomprising modular code blocks of at least two different sizes, andfurther comprising a searcher for searching for a user equipmentspecific identifier in the modular structure of the at least one controlchannel, wherein the modular structure forms a tree where each of themodular code blocks defines one node of the tree, respectively, whereineach of the nodes comprises signalling entries coded by a given coderate, wherein the modular structure of the at least one control channelallows user equipment specific separate coded control channels withlimited and optimized number of searches, and wherein the signallingentries include information blocks, and each information block of asignalling entry is rate matched to a node of the tree.
 5. An apparatus,comprising: a receiver configured to receive at least one controlchannel allocated at least to a user for at least one of uplink anddownlink directions in a network, which the at least one control channelis arranged as at least a part of a modular structure comprising modularcode blocks of at least two different sizes; and a processor configuredto search for an appropriate code block in the modular structure of theat least one control channel, wherein the modular structure forms a treewhere each of the modular code blocks defines one node of the tree,respectively, wherein each of the nodes comprises signalling entriescoded by a given code rate, wherein the modular structure of the atleast one control channel allows user equipment specific separate codedcontrol channels with limited and optimized number of searches, andwherein the signalling entries include information blocks, and eachinformation block of a signalling entry is rate matched to a node of thetree.
 6. The apparatus according to claim 5, including a plurality ofcontrol channels to be allocated to users for at least one of uplink anddownlink direction in a network, which control channels are arranged asa tree comprising nodes of modular code blocks on at least two differentlevels with each code block defining one control channel at a node ofthe tree.
 7. The apparatus according to claim 6, wherein the code blocksof different levels have different sizes.
 8. The apparatus according toclaim 5, wherein the tree is a binary tree.
 9. The apparatus accordingto claim 5, wherein each node of the tree corresponds to a predeterminedset of sub-carrier symbols.
 10. The apparatus according to claim 5,wherein the tree is a tree of variable code rates.
 11. The apparatusaccording to claim 5, wherein the at least one control channel isprovided for signalling.
 12. The apparatus according to claim 11,wherein each of the signalling entries comprise a unified entry format.13. The apparatus according to claim 11, wherein at least some of thesignalling entries are of different types.
 14. The apparatus accordingto claim 11, wherein the signalling entries include information blocks,and at least some of the signalling entries have a different informationblock length.
 15. The apparatus according to claim 14, wherein an uplinksignalling entry comprises an information block length which is part, inparticular half, of the information block length of a downlinksignalling entry.
 16. The apparatus according to claim 5, wherein thetree is dimensioned according to a system bandwidth and/or according topredetermined channel code rates.
 17. The apparatus according to claim5, wherein the tree is pruned to include a sub-set of nodes of allpossible nodes only.
 18. The apparatus according to claim 5, wherein acode block in a level of higher order has a smaller size than a codeblock in a level of lower order.
 19. The apparatus according to claim 5,wherein power from a resource provided for a code block which iscurrently not used is available for at least another code blockcurrently used.
 20. The apparatus according to claim 5, wherein at leasta part of transmission power from a code block resource on sub-carriersin a node of the tree is available to be used on sub-carriers in anothernode of the tree.
 21. A method, comprising: receiving, by a receiver ofan apparatus, at least one control channel allocated at least to a userfor at least one of uplink and downlink directions in a network, whichthe at least one control channel is arranged as at least a part of amodular structure comprising modular code blocks of at least twodifferent sizes; and searching, by a processor of the apparatus, for anappropriate code block in the modular structure of the at least onecontrol channel, wherein the modular structure forms a tree where eachof the modular code blocks defines one node of the tree, respectively,wherein each of the nodes comprises signalling entries coded by a givencode rate, wherein the modular structure of the at least one controlchannel allows user equipment specific separate coded control channelswith limited and optimized number of searches, and wherein thesignalling entries include information blocks, and each informationblock of a signalling entry is rate matched to a node of the tree. 22.The method according to claim 21, including a plurality of controlchannels to be allocated to users for at least one of uplink anddownlink direction in a network, which control channels are arranged asa tree comprising nodes of modular code blocks on at least two differentlevels with each code block defining one control channel at a node ofthe tree.
 23. The method according to claim 21, wherein the code blocksof different levels have different sizes.